For example, MEMS (micro electro mechanical systems) applications frequently require signal amplifiers having a small space requirement, low input capacitance, high input impedance, a low current requirement and low noise. A rail-to-rail AB output stage, current feedback and input signal levels up to the supply voltage, for example, an input signal referencing a negative or supply potential, are also desirable.
Typically, a sufficient gain can be provided with a differential amplifier, which comprises a voltage divider with feedback on its output side.
However, with typical applications, a voltage offset or low frequency noise is present to some extent at the input of such an amplifier. For example, with such amplifiers, a changing voltage offset of a variable input signal is also amplified. This can lead to, among others, a degradation of the signal quality in the amplified output signal. In addition, the current consumption in the amplifier is increased due to the amplification of the low frequency noise or of the voltage offset.
Low frequency components can be suppressed, for example, through capacitive decoupling. For this however, it is necessary, depending on a desired frequency suppression, to use relatively large capacitance values, which increases the cost of such an amplifier circuit, or alternatively, larger resistance values for the voltage divider, which negatively impact the noise performance of the amplifier circuit.